Multi-element anode structures for electrochemical cells

ABSTRACT

Anode structures for primary electrochemical cells. An anode structure in accordance with a first embodiment of the invention includes a metal screen (e.g., of nickel) and a plurality of spaced-apart lithium anode elements arranged in a predetermined pattern (e.g., row and column) and embedded within the metal screen. A metal frame is connected with and surrounds the metal screen and has an electrical terminal extending therefrom. 
     An anode structure in accordance with a second embodiment of the invention is similar to that of the first embodiment with the exception that the spaces between the lithium anode elements of the anode structure of the second embodiment are filled with a heat-absorbing porous insulative separator material.

CROSS REFERENCE TO RELATED APPLICATION

In co-pending application Ser. No. 319,813, filed concurrently herewithin the name of Franz Goebel and entitled METHOD FOR FABRICATINGMULTI-ELEMENT ANODE STRUCTURES FOR ELECTROCHEMICAL CELLS, there isdisclosed and claimed methods for fabricating multi-element anodestructures for electrochemical cells as disclosed and claimed in thepresent application.

BACKGROUND OF THE INVENTION

The present invention relates to anode structures and, moreparticularly, to anode structures for primary electrochemical cells.

Primary electrochemical cells are generally well known and understood bythose skilled in the art. One particularly useful primaryelectrochemical cell, especially for high current drain applications, isa so-called prismatic primary electrochemical cell. Such a cell isdescribed in detail in U.S. Pat. No. 4,086,397, in the names of FranzGoebel and Nikola Marincic, and includes a battery stack enclosedtogether with an electrolytic solution within a metal housing. Thebattery stack as used within the cell comprises a large number ofgenerally rectangular cell components including a plurality of anodestructures, carbon cathode current collector electrodes, and insulativeseparators (e.g., of fiberglass) between the anode structures and thecarbon cathode current collector electrodes. Each anode structuregenerally comprises a large rectangular, flat, single, continuous sheetof an oxidizable alkali metal, such as lithium, physically impressedinto a flat supporting expanded metal (e.g., nickel) grid, and each ofthe carbon cathode current collector electrodes comprises an aggregationof porous, semi-rigid carbon globules or conglomerates physicallyimpressed into a flat expanded metal (e.g., nickel) current collectorgrid. A common and preferred electrolytic solution employed in the cellas described above is a cathodelectrolyte solution comprising areducible soluble cathode such as thionyl chloride and an electrolytesolute such as lithium tetrachloroaluminate dissolved in the thionylchloride.

By the appropriate selection of battery cell components and materials, acell as described above can be constructed to have any one of severalpossible sizes and energy configurations. A typical cell, for example,has exterior dimensions of approximately 18 inches (height)×13 inches(width)×10 inches (depth), a weight of 156 pounds, an ampere-hourcapacity rating of 10,000 ampere-hours, and a nominal discharge currentof 40 amperes.

In an electrochemical cell as described hereinabove, it is possibleunder certain adverse conditions, for example, in the case of severephysical abuse to the cell, for an internal short circuit condition todevelop within the cell between metal parts of a pair of anode andcathode structures. In such a case, a hot spot can develop in thelithium sheet of the anode structure and propagate throughout the sheet.If the sheet temperature is high enough, for example, above 180° C., thelithium metal can melt and react violently with the thionyl chloride, orwith components of the discharge reaction such as sulfur, or both,resulting in severe, permanent physical damage to the cell.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, an anode structure is providedfor an electrochemical cell which offers increased protection againstpropagation of hot spots in lithium metal when employed in anelectrochemical cell. An anode structure in accordance with a firstembodiment of the invention includes a metal screen and a plurality ofspaced-apart discrete lithium anode elements arranged in a pattern andin physical contact with the metal screen. An anode structure inaccordance with a second embodiment of the invention includes a metalscreen, a plurality of spaced-apart discrete lithium anode elementsarranged in a pattern and in physical contact with the metal screen, andan insulative separator material disposed between the lithium anodeelements and in physical contact with the metal screen. In bothembodiments of the anode structures, the spacing of the lithium anodeelements in the screens minimizes or reduces the possibility of thepropagation of hot spots.

BRIEF DESCRIPTION OF THE DRAWING

Various objects, features and advantages of anode structures forelectrochemical cells in accordance with the present invention will beapparent from a detailed discussion taken in conjunction with theaccompanying drawing in which:

FIG. 1 is a partially exploded perspective view, with parts broken away,of a primary electrochemical cell employing anode structures inaccordance with the present invention;

FIG. 2 illustrates an anode structure in accordance with a firstembodiment of the invention;

FIG. 3 is a cross-sectional view, taken along the line 3--3 in FIG. 2,of the anode structure of FIG. 2;

FIG. 4 illustrates an anode structure in accordance with a secondembodiment of the invention; and

FIG. 5 is a cross-sectional view, taken along the line 5--5 in FIG. 4,of the anode structure of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown a primary electrochemical cell 1employing a plurality of anode structures 2 in accordance with thepresent invention. The electrochemical cell 1, and the electrochemicalsystem therefor, may be constructed in accordance with the teachings ofthe aforementioned U.S. Pat. No. 4,086,397 and generally includes arectangular metal housing 3, a battery stack 4 disposed within thehousing 3, an electrolytic solution 5 in contact with the battery stack4, and a top cover assembly 6. The housing 3 may be of stainless steeland have typical outer dimensions of approximately 18 inches (height)×13inches (width)×10 inches (depth). The battery stack 4 as employed withinthe housing 3 comprises a plurality of generally-rectangular cellcomponents. These components include, in addition to the aforementionedplurality of anode structures 2, a plurality of carbon cathode currentcollector electrodes 8, and a plurality of insulative separators 10between the anode structures 2 and the carbon cathode current collectorelectrodes 8. Although not specifically shown in the drawing, each ofthe carbon cathode current collector electrodes 8 comprises anaggregation of porous semi-rigid carbon globules or conglomeratespressed into a flat expanded metal (e.g., nickel) grid or screen to besupported thereby. The grids of the electrodes 8 also serve as currentcollector members for the cell 1 during the discharge of the cell. Theseparators 10, which serve to electrically isolate the anode structures2 from the carbon cathode current collector electrodes 8, may be of asuitable insulative material such as fiberglass. The anode structures 2and the carbon cathode current collector electrodes 8 further havenarrow portions or rails 12 at the peripheries thereof from which thinmetal rectangular tabs 13 extend upwardly for facilitating the physicaland electrical connection of the anode structures 2 and the carboncathode current collector electrodes 8 to corresponding metal (e.g.,nickel) bus bar arrangements 14 and 15, respectively. The bus bararrangements 14 and 15 are in turn mechanically and electricallyconnected to a pair of metal (e.g., nickel) terminals 17 and 18,respectively, located in, and insulated from, the top cover assembly 6.

Typical dimensions for the battery stack 4 as described hereinabove,corresponding to a total of 47 anode structures and cathode electrodes,are approximately 14.5 inches (height)×12.8 inches (width)×9.8 inches(depth). The electrolytic solution 5 to which the battery stack 4 isexposed and which is compatible with the cell components as describedhereinabove is preferably a cathodelectrolyte solution comprising areducible soluble cathode such as thionyl chloride and an electrolytesolute such as lithium tetrachloroaluminate dissolved in the thionylchloride.

Each of the anode structures 2 as described briefly hereinabove may takethe form as shown at 2a in FIGS. 2 and 3 or at 2b in FIGS. 4 and 5. Theanode structure 2a as shown in FIGS. 2 and 3 comprises a plurality ofdiscrete lithium anode elements 20 embedded within, and physicallysecured to, a flat rectangular metal grid or screen 21 in aspaced-apart, equi-distant, row and column format. As shown in FIGS. 2and 3, each of the lithium anode elements 20 has a generally cylindricaloverall configuration and a generally circular cross section, althoughmany other shapes are possible, e.g., square, rectangular, oval, etc. Inaddition, a variety of patterns or layouts other than a row and columnpattern may be used.

The lithium anode elements 20 as shown in FIGS. 2 and 3 are selected tohave physical dimensions and spacings therebetween such that any hotspot which might occur in any one of the elements 20, for example, as aresult of an internal short circuit condition within the associatedcell, does not propagate or spread to the other lithium elements 20 andresult in melting of the elements 20 and consequential violent reactionwith other components or discharge reaction products within the cell. Inthe particular embodiment of the anode structure shown in FIGS. 2 and 3,the spaces between the lithium anode elements 20 are occupied by theelectrolytic solution when the anode structure is actually in placewithin the cell.

The grid or screen 21 within which the lithium anode elements 20 areembedded is surrounded by a metal (e.g., nickel) frame 22 with anassociated tab 13 and may take the form of an expanded metal (e.g.,nickel) substrate having interconnected portions 21a defining a largenumber of openings 21b therein. The lithium anode elements 20, which aresofter than the material (nickel) of the screen 21, are pressed into theportions 21a and openings 21b of the screen 21 in a spaced-apartfashion. The anode elements 20 as employed with such a screen may have atypical diameter of 1/4 inch and a thickness of 0.040 inch. Theparticular spacing between the elements 20 depends on the ability of theelements to absorb heat and not transfer the heat to adjacent anodeelements. A typical spacing for the elements 20 having theabove-specified dimensions is 1/8 inch. A typical thickness for thescreen 21 is 0.005 inch.

The anode structure 2b as shown in FIGS. 4 and 5 is similar to thatshown at 2a in FIGS. 2 and 3 with the exception that the lithium anodeelements of the anode structure 2b, shown at 25 in FIGS. 4 and 5, have aporous insulative separator material 26 physically interposed betweenthe lithium anode elements 25. Both the anode elements 25 and thematerial 26 are pressed within metal portions 27a and openings 27b of aflat expanded metal screen 27 (FIG. 5). The insulative material 26 maytake the form of a fiberglass powder, a silicate, alumina, or mixturesthereof, or any other suitable insulative separator material, eitheralone or together with a suitable binder such as "Halar" (ethylenechlorotrifluoroethylene, or ECFE) in low concentration. The size andspacing of the lithium anode elements 25 in this case depends on theability of the anode elements 25 and the separator material 26 to absorbheat. The separator material 26 is pressed into the grid or screen 27 inany suitable manner, for example, by rolling the material across andinto the screen 27, preferably from both sides. Since the separatormaterial 26 is porous in nature, any covering of the lithium anodeelements 26 by the separator material 26 is not harmful since theelectrolytic solution in the associated cell is able to penetrate theseparator material and make contact with the anode elements 25.

Suitable techniques for constructing and assembling the anode structures2a and 2b shown in FIGS. 2-5 and described hereinabove are disclosed indetail and claimed in the aforementioned co-pending application Ser. No.319,813.

While there has been described what are considered to be preferredembodiments of the invention, it will be apparent to those skilled inthe art that various changes and modifications may be made thereinwithout departing from the invention as called for in the appendedclaims.

What is claimed is:
 1. An anode structure for an electrochemical cell,comprising:a metal screen; and a plurality of spaced-apart discretelithium anode elements arranged in a pattern and in physical contactwith the metal screen.
 2. An anode structure in accordance with claim 1wherein:the metal screen is of a predetermined thickness and hasinterconnected portions defining a plurality of openings in the screen;and the lithium anode elements are embedded within the screen by way ofthe interconnected portions and openings in the screen.
 3. An anodestructure in accordance with claim 2 wherein:the metal screen is a flatexpanded metal screen.
 4. An anode structure in accordance with claim 3wherein:the plurality of lithium anode elements are arranged in apattern of rows and columns.
 5. An anode structure in accordance withclaim 4 wherein:the lithium anode elements in each row are spaced apartfrom each other by an equal distance.
 6. An anode structure inaccordance with claim 2 wherein:each of the lithium anode elements has agenerally cylindrical configuration and a generally circular crosssection.
 7. An anode structure in accordance with claim 2 furthercomprising:a metal frame connected with and surrounding the metal screenand having an electrical terminal extending therefrom.
 8. An anodestructure in accordance with claim 1 further comprising:a porousinsulative separator material disposed between the lithium anodeelements and in physical contact with the metal screen.
 9. An anodestructure in accordance with claim 8 wherein:the porous separatormaterial is selected from the group consisting of alumina, fiberglass, asilicate, and mixtures thereof.
 10. An anode structure in accordancewith claim 8 wherein:the metal screen is of a predetermined thicknessand has interconnected portions defining a plurality of openings in thescreen; and the lithium anode elements and the separator material areembedded within the screen by way of the interconnected portions andopenings in the screen.
 11. An anode structure in accordance with claim10 wherein:the metal screen is a flat expanded metal screen.
 12. Ananode structure in accordance with claim 11 wherein:the plurality oflithium anode elements are arranged in a pattern of rows and columns.13. An anode structure in accordance with claim 12 wherein:the lithiumanode elements in each row are spaced apart from each other by an equaldistance.
 14. An anode structure in accordance with claim 10wherein:each of the lithium anode elements has a generally cylindricalconfiguration and a generally circular cross section.
 15. An anodestructure in accordance with claim 10 further comprising:a metal frameconnected with and surrounding the metal screen and having an electricalterminal extending therefrom.